An image forming apparatus such as a copying machine optically reads an image of an document set on an document setting plate via a transparent document setting plate by moving and lighting an exposure lamp along the document setting plate. The read image is printed on a copy paper, which is an image forming medium.
As an example of the exposure lamp, there are a halogen lamp and a cold-cathode ray tube. While the halogen lamp is high in a calorific value, the cold-cathode ray tube is low in the calorific value. When this cold-cathode ray tube is used, thermal effects (deformation, fracture and the like) on the surrounding parts can be prevented.
However, the cold-cathode ray tube requires about five minutes from the time it is lit until the quantity of light is sufficiently stabilized. For this reason, when the cold-cathode ray tube is adopted as an exposure lamp, in order to prevent a delay in the start of reading, the cold-cathode ray tube is lit even in a standby time except for a reading time.
Nevertheless, when the cold-cathode ray tube is lit in a standby time, on the occasion when a user opens the document setting plate cover in order to set an document on the document setting plate, the light of the cold-cathode ray tube flows into user's eyes via the document setting plate so that a user feels dazzled.